Double effect absorption refrigeration machine



2 Sheets-Sheet 1 BY /ohw G. A75/Q fr. ///A/ MCAD# Aug. 16, 1966 J, G. REID, .1R

DOUBLE EFFECT ABSORPTION REFRIGERATION MACHINE Filed Aug. 2, 1965 FIGA.

J. G. REID, JR

Aug. 16, 1966 DOUBLE EFFECT ABSORPTION REFRIGERATION MACHINE 2 Sheets-Sheet 2v Filed Aug. 2, 1963 FIE E United States Patent Office 3,266,266 Patented August 16, 1956 3,266,266 DOUBLE EFFECT ABSDRPTIN REFRIG- ERATIQN MACHINE John Graham Reid, Jr., Grosse Pointe, Mich., assignor to American Radiator & Standard Sanitary Corporation, New York, NKY., a corporation of Delaware Filed Aug. 2, 1963, Ser. No. 299,547 `7 Claims. (Cl. 62--476) This invention relates `to an absorption refrigeration machine of the double effect type, i.e., a machine wherein refrigerant is released from absorbent solution in two generating stages.

One object of the invention is to provide a double effect refrigeration machine particularly suited for construction as a large capacity unit, as for example over 100 tons of refrigerating effect.

A further object is to provide a double effect machine which can be controlled with a relatively simple low cost control system.

An additional object is to provide a double effect machine which is not apt to malfunction during operational periods or shutdown periods.

Another object is to provide a double effect machine wherein the solution concentrations are maintained within prescribed values in the different parts of the machine. Thus, I have designed the machine so that during shutdown periods the refrigerant and absorbent solutions are trapped in specified chambers, whereby the refrigerant and solutions are precluded from mixing together to alter their character. This arrangement provides improved efficiency as well as protection of the system from crystallization of absorbent due to overconcentration.

Other objects of this invention will appear from the following description and appended claims, reference being had to the accompanying drawings forming a pant of this specification wherein like reference characters designate corresponding parts in the several views.

In the drawings:

FIGURE 1 is a view of one embodiment of the invention, partly schematic and partly taken on section tline 1-1 in FIG. 2; and

FIG. 2 is a sectional view taken on line 2 2 in FIG. l.

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

GENERAL ARRANGEMENT In FIG. l of the drawings there is shown an absorption refrigeration machine comprising a rst refrigerant vapor generator 10, a second refrigerant vapor generator 12, a refrigerant condenser 14, a refrigerant evaporator 16, and a refrigerant absorber 18. The illustrated machine is particularly designed to use Water as the refrigerant and lithium bromide as the absorbent, although other refrigerants and absorbents could be employed in practice of the invention. In FIG. l of the drawings the lithium bromide concentration is shown as varying from 57% to 63% in the different parts of the machine. Illustrative flow rates and temperatures are also shown on the drawlugs.

In operation, a 57% solution of refrigerant and absorbent is introduced to generator 10 through a liquid line to provide a solution level 22 in the generator shell 24. Heat is applied to the solution through the firetubes 70 and 26, thus expelling refrigerant from the solution.

The expelled refrigerant vapor is directed into a vapor line 28 which ultimately feeds same to heat exchange tubes 30 in the shell 38 for the second generator 12.

The overflow of relatively refrigerant-weak solution in shell 24 is directed into a liquid line 32 and is passed through heat exchanger 29 before introduction to generator 12 through the liquid supply line 34. Liquid solution from line 34 is thermally engaged with the refrigerant vapor in tubes 30 by dripping the solution onto the outer surfaces of the tubes, thereby causing a substantial portion of the refrigerant in the tubes to be condensed and c01- lected in a chamber 36.

As the refrigerant-absorbent solution flows gravitationally over the outer surfaces of tubes 30 additional refrigerant vapor is released within the shell 38. This vapor is automatically directed over the cold water tubes 40 of the condenser 14 to collect as condensed refrigerant in the trough 42. The trough 42 refrigerant is then combined with the chamber 36 refrigerant and fed to a restriction device 44.

After passing through restriction device 44 the refrigerant is directed into a dripper mechanism 46 located in shell 120 above the chilled water tubes 48 of evaporator 16. Heat is thereby extracted from the water in the tubes to vaporize the refrigerant on the tube outer surfaces. Any unvaporized refrigerant collects in trough 50 and recirculates back to the dripper mechanism via a line 52 and pump S3. The vaporized refrigerant in shell 120 is automatically directed toward the internally cooled tubes 54 of absorber 18.

Meanwhile refrigerant-weak absorbent solution which has collected in the bottom of shell 38 is directed through a line 56 to heat exchanger 58 and thence into a line 60 where it is distributed in drip form onto the exterior surfaces of the absorber tubes 54. The refrigerant vapor is thereby absorbed by the liquid absorbent and discharged as refrigerantrich solution through line 62. The cycle is completed by pumping the refrigerant-absorbent solution back to the rst -generator 10 via line 63, heat eX- changers 58 and 29, line 64, and line 20.

Generator 10 As shown in FIG. 1, the generator comprises a horizontal cylindrical shell 24. As seen in FIG. 2 this shell extends between two vertical sheets or plates 66 and 68. Disposed within shell 24 is a relatively large diameter retube 70 and a series of smaller retubes 26. Tube 70 extends beyond tube sheet 66 through a smoke flue 72 to accommodate a conventional burner 74 which may be eitther an oil burner, gas burner or combination gas-oil burner. During operation the burner directs a llame through tube 70 to the insulated chamber 76 which communicates with the open ends of tubes 26. The hot gases are thus directed through tubes 26 in the arrow 78 direction to ultimately be exhausted through llue 72.

Liquid solution is admitted to shell 24 through line 64, an upright chamber 65, and line 20. Chamber 65 is vented to the upper portion of shell 24 via a line 67. Solution is withdrawn from shell 24 through an overflow chamber 69 and line 32. The solution is thereby maintained at level 22, both during operational periods and shutdown periods. Thus, during shutdown periods the shell 24 liquid cannot back up through line 64 because line 20 constitutes a trap for the liquid, and line 67 equalizes the pressure in chamber 65 and shell 24. As a result solution is maintained in the generator during shutdown periods.

Disposed within the upper portion of shell 24 is an eliminator which functions to prevent entrained drops of liquid solution from passing into vapor pipe 28. In the illustrated form the eliminator comprises a vertical wall 82 and two angular apertured walls 84 arranged so that Vapor and any entrained liquid must pass through the apertures and double back on itself as it enters tube 28. Most of the entrained liquid is thus separated by inertia action and drains back into the pool of solution in shell 24. Vapor tube 28 extends from shell 24 to an additional 'liquid eliminator chamber 86 located at the rear of shell 38.

Second-effect generator .Z2-condenser 14 As shown in FIG. 1, second-effect generator 12 and condenser 14 are disposed within a single cylindrical shell 38. As shown in FIG. 2 this shell extends between a front tube sheet 88 and a rear tube sheet 98. The secondeffect generator heat transfer tubes 30 extend within shell 38 through tube sheets 88 and 90 so that their opposite open ends communicate with chamber 86 and the chamber defined by header 92. The eliminator is provided with an upstanding partition 94 so that vapor is discharged downwardly from tube 28 into the space to the right of the partition. The vapor must therefore execute a reverse upward turn before it can enter tubes 30. As a Iresult any remaining entrained liquid droplets are separated from the vapor and collect in the lower portion of chamber 86. A pipe 96 connects chamber 86 with the interior of shell 38 so that separated liquid is automatically returned to the system. A restriction is provided in pipe 96 to maintain a pressure differential between chamber 86 and the interior of shell 38.

As best seen in FIG. l, header 92 is provided with a partition comprising a horizontal wall 98 and a vertical wall 100, said partition forming separate chambers 102 and 36. Tubes 30 discharge into chamber 102 so that refrigerant must pass through the restriction orice 106 in wall 98 before reaching chamber 36. Any vapor in chamber 36 is exhausted into shell 38 via an opening 114 formed in tube sheet 88.

As previously noted the liquid solution from first effect generator is directed into line 32 and is ultimately fed to second effect generator 12 via a line 34. A fixed or adjustable restriction 108 may be provided in line 34 to maintain a desired pressure differential between generators 18 and 12. Line 34 includes a tube 34' which extends horizontally within shell 38 above three separate rectangular receptacles 110 disposed at spaced points along the shell length. Suitable openings are formed in the tube to gravitationally feed solution from line 34 to the receptacles. The tube-receptacle arrangement is preferably the same as that shown at 140 and 138 in the evaporator.

Extending between receptacles 110 are a se-ries of openended dripper pipes 112 having spaced apertures along their upper surfaces; in an illustrative construction the apertures are spaced about one-half inch apart for the entire pipe length. With such an arrangement the refrigerant-absorbent solution fills the pipes and oozes out of the pipe openings to flow downwardly around the pipe outer surface, whereby to drip onto the outer surfaces of heat ex-change tubes 30. The heat exchange tubes are thus supplied with relatively cool solution on their outer surfaces, and relatively hot vapor on their inner surfaces (from chamber 86).

In an illustrative arrangement the refrigerant vapor within tubes 30 may have a temperature of about 322 and the solution on the tube outer surfaces may have a temperature of about 196. Due to this temperature differential the vapor within tubes 30 is condensed and collects in chamber 36 as liquid refrigerant. The exchange of heat causes refrigerant in the solution on the tube outer surfaces to vaporize and pass over to the tubes 40 which form condenser 14. Any vapor formed by flashing through orifice 106 is exhausted from chamber 36 via the relatively large opening 114 in tube sheet 88, thus comingling with the refrigerant vapor in shell 38. The absorbent-rich solution dripping down the tubes 30 outer surfaces collects in the bottom of shell 38 and discharges through line 56.

Condenser tubes 40 are supplied with coolant through two -conventional headers, one of which is shown at 116 in FIG. 2. The illustrated arrangement is a single pass arrangement wherein the coolant (preferably water) flows from a header on tube sheet 98 through all of the tubes 48 to the outlet header 116 mounted on tube sheet 88. A conventional cooling tower may be utilized to receive the coolant before recirculation back to the refrigeration machine absorber.

In operation, the relatively cool condenser tubes 40 cause refrigerant vapor in shell 38 to condense on the outer surfaces of the tubes and drip downwardly into the trough 42 which extends the full length of shell 38. A suitable discharge line 118 is provided for directing the condensed refrigerant into a tubular member 44. Additional condensed refrigerant is received from chamber 36 via a line 119.

Evaporator 1li-absorber 18 As shown in FIG. 1, the evaporator and absorber are both disposed within la cylindrical shell 120. This shell is located between two upstanding tube sheets 122 and 124-. Evaporator tubes 48 extend horizontally between the two tube sheets to communicate with a front header 127 and a rear header 128, the arrangement permitting relatively high temperature heat exchange liquid to enter fitting 138, ow through the lowermost ones of tubes 48 to header 128, and return to outlet fitting 132 via the uppermost ones of tubes 48. Water is usually used as the heat exchange liquid; in one arrangement it enters fitting 130 at about 55, is chilled in tubes 48, yand leaves through fitting 132 at -about 45. The chilled water is then circulated to individual air conditioning units or other cooling load before returning to machine inlet 130 as 55 water.

The water chilling operation is performed by the evaporation of refrigerant on the outer surfaces of tubes 48. As previously indicated, the refrigerant is supplied to the evaporator through la tubular chamber member 44. The necessary pressure differential lbetween the condenser 14 and evaporator 16 can be maintained by a restriction orifice 134 formed at the discharge end of line 118. The chamber in member 44 is preferably maintained at a relatively low pressure, as for example .1 p.s.i.a. by equalization in pressure with shell 16 through pipe 121.

Liquid refrigerant is allowed to gravitationally ilow from chamber 44 through line 136 to a horzontal tube 138 located in the upper portion of shell 16. Disposed below tube 138 are three open-topped receptacles 140 which communicate with openings 142 in the tube to receive the liquid refrigerant and feed same to a series of horizontal refrigerant distributor pipes 144. The distributor pipes are provided with apertures 146 in their upper surfaces so that liquid refrigerant is caused to ooze out of the pipes and ow down around the pipe outer surfaces before dripping onto the subjacent heat exchange tubes 48. The number of pipes 144 corresponds to the number of verti-cal rows of tubes 48 so that each row of heat exchange tubes is supplied with liquid refrigerant from the overlying pipe 144.

It is -contemplated that the refrigerant will be evaporated by the time it has reached the lowermost heat exchange tube in each vertical row. However, any excess liquid refrigerant which drips from the lowermost heat exchange tubes is collected in trough 50 and discharged through line 52. A suitable pump 53 may be provided to recirculate the refrigerant back to member 44 for return to the system. In some cases this pump may not be necessary.

The refrigerant evaporated from around tubes 48 is automatically caused to pass over to the heat exchange tubes 54 of absorber 18. Coolant, such as water, is supplied to the exchange tubes 54 by a rear header 148 having an inlet fitting 150. The coolant passes from tting 150 through the lowermost ones of tubes 54 to a front header 152 and returns through the uppermost ones of tubes 54 to an outlet fitting 156. A bafe 158 in header 148 causes the coolant to ow in two passes through the heat exchange tubes. Other pass arrangements may be provided by suitable baffling of the headers. Preferably the coolant enters fitting 150 at about 85 and leaves through fitting 156 at about 95. It is then directed to the condenser tubes 40 and further raised to about 98 therein.

Absorbent solution at about 63% LiBr concentration is supplied to the absorber through a line 60 which includes a horizontal tube 159 disposed within shell 120. Positioned below tube S are three open-topped receptacles 160 spaced similarly to the receptacles 140. Suitably apertured distributor pipes 162 are disposed between troughs 160 to drip the liquid solution onto the heat exchange tubes 54, whereby the solution is cooled to absorb the refrigerant vapor issuing from evaporator 16. A suitable partition 164 may be provided in shell 120 to prevent intermingling of the absorbent with the refrigerant on evaporator tubes 48. Thus any splashed solution from tubes 54 is directed against partition 164 without passing over to tubes 48. A similarly functioning partition 164 is provided in shell 38 for battling the splash from tubes 30.

During the refrigerant-absorption process the refrigerant has its temperature raised from about 40 to about 102, and the absorbent has its temperature lowered from about 130 to 102, due to the flow of coolant through tubes 54. The refrigerant-rich solution collects in the bottom of shell 120 and is discharged through line 62 to a solution pump 166.

During operational periods solution pump 166 is continually driven to direct solution `through a modulatingr valve 170 into lines 63 and/or line 168. The line 63 solution is fed through heat exchangers 58 and 29 to line 64 so that its temperature is raised from about 102 to about 265 when it reaches generator 24. Line 168 solution is fed to Iline 60 and .thence recirculated over the absorber tubes.

CONTROL OF THE MACHINE Preferably the refrigeration system is =a modulated system wherein the flow of solution and 'fuel input is modulated in accordance with the need for refrigeration. Therefore, the output of pump 166 is apportioned between lines 168 and 63 in accordance with refrigeration needs, as 'sensed at the chilled water outlet 132. The apportioning function is preferably accomplished by a standard motor-operated metering or modulating valve 170. The modulation of fuel is accomplished by a standard modulating valve (not shown).

At fu-ll refrigeration load valve 170 is controlled so that substantially all of the 57% solution from the absorber flows through line 63. At partial loads the valve is controlled to direct part of the 'solution into line 168, from whence it can proceed to line 60 and recirculate through the absorber along with the solution from heat exchanger 58.

The operation at partial refrigeration loads involves a relatively small flow of refrigerant-rich solution in line 64 so that less refrigerant is `available in the solution supplied to the first generator. The flow of heat to the first generator is controlled in proportion to the flow of solution through line 64 so that the generator at al-l times has about lthe same outgoing solution concentration, as for example 61%. The modulating action causes relatively small quantities of refrigerant -to be expelled from the generator solution at partial loads so that less refrigerant flows through vapor pipe 28, and less solution is discharged through line 32. The amount of refrigerant .supplied to chamber 44 and evaporator tubes 48 is thereby curtailed at partial loads.

Changes in load may be sensed by various means, as for example a thermostatic bulb responsive to the chilled water temperature issuing from outlet fitting 132. An increase in chilled water ltemperature above the design temperature causes the bulb charge to expand and operate a suitable bellows or diaphragm control. The control can comprise a standard potentiometer arrangement wherein a potentiometer slider is operated. to vary the resistance of one ann of a balanced bridge circuit located in the control circuitry for valve 170 and the fuel valve of burner 74. Preferably the solution valve and lburner fuel supply valve are operated in unison from a single sensing bulb to maintain desired refrigeration output without any concentration imbalances` or hunting. The construction of the machine makes for a relatively simple low cost control system.

FEATURES OF THE INVENTION One feature of this invention resides in the: employment o-f a direct red tube-shell boiler for lthe first generation of refrigerant vapor. Previously large size single effect refrigeration machines have employed tube-shell heat exchangers as vapor generators. However the tubes were usually supplied with steam as the heating medium, whe-reas the present construction as shown. in FIGS. l and 2 utilizes direct flame as the heat source. The temperatures necessary in the generator of a double effect system are relatively high, as for example 322, and relatively high pressure steam is necessary to :achieve such temperatures. Where such high pressure stearn is not economically available the pre-sent direct fired arrangement is advantageous over steamlheated systems.

Certain small size double effect units have been :constructed using direct fire, but usually the generators have involved vertical tubular heaters wherein both the solution and vapor are lifted upwardly toward the generator discharge outlet. Considerable liquid is entrained with the vapor so that comparatively imperfect liquid separation is attained. Additionally, these vertical heaters are not particularly suited to handling the large quantities of solution required in large capacity units. The use of a direct fired horizontal tube-shell arranged as the first effect generator is mulch preferred.

The present invention :as shown in the illustrative drawings comprises a horizontal tube-shell .generator 10 having a solution level 22 above the point of Iadmission 34 ofthe solution into the .second generator 12. This heighth relationship is particularly important in that it precludes flooding of the first generator, particularly during startup periods. During start-up the burner 74 and solution pump 166 are energized simultaneously so that considerable solution may circulate through the system before the first generator comes up to operating temperature. With the first effect generator disposed 'as the most elevated component in the system the initial flow of solution into the first generator can be accommodated by overflow into line 32 without any flooding of the generator.

A further novel feature of this invention is the arrangement whereby chambers 102 and 36 are formed at the outlet ends of generator tubes 30 so that condensed refrigerant can be economically collected and reintroduced to the system. Chamber 36 also constitutes a flash chamber for returning uncondensed refrigerant to the outer surfaces of the condenser tubes 40 where i't can readily condens-e.

Preferably generator 12, evaporator 16, and absorber 18 are constructed .as horizontal tube bundles and are arranged below individual dripper devices, whereby the solution or pure refrigerant is distributed as discrete droplets onto the tube outer surfaces. Such distribution arrangements -are much preferred to the conventional spray arrangements because of the improved operating efficiencies and reduced bypassing of the tube surfaces. As shown in .the drawings the tube bundles are preferably separated from one another by considerable distances and by baffles to prevent undesired comingling of the fluids, las by .splash from the tube surfaces.

Preferably the components are constructed in three .separate cylindrical shells .to permit adequate spacing of the tube bundles and proper gravitational flow of solution without a multiplicity of pumps 'or complex controls.

What is claimed:

1. In an absorption refrigeration machine comprising a first -generator and a second generator arranged so that refrigerant v-apor 4from the first generator and refrigerantabsorbent solution from the first generator pass in rheat exchange relation with one another in lthe second generautor lto release additional refrigerant vapor from the solution: the improvement comprising the formation of the first generator as a first horizontal solution shell having a series of horizontal firetubes located below the solution level; said second generator comprising a second horizontal shell, land a .series of heat exchange tubes extending within the second shell below the solution level in the first shell; means for passing refrigerant vapor from the first generator into the second generator tubes; conduit means 'for gravitationally passing liquid refrigerant-absorbent .solution from the first shell into the second shell and `over the outer .surfaces of the second generator theat exchange tubes to release refrigerant from the solution; means for receiving condensed refrigerant from the second generator tubes comprising a rst chamber located .at the outlet ends of the tubes, a `second chamber, and a restricted passage between the rst and second chambers for passing condensed refrigerant and flashed vapor into the second chamber; .and an additional passage between the second chamber and interior of the second generator shell to permit flashed vapor 'to pass into the second shell.

Z. A double effect .absorption refrigeration machine comprising a first generator which includes .a horizontal solution shell having a series of horizontal firetubes located -below the solution level; la second horizontal shell having two horizontal tube bundles therein, one of said tube bundles forming a refrigerant generator, land the other tube bundle forming a refrigerant condenser; said tube bundles being located below the solution level in the first shell; means for passing refrigerant vapor from the first generator into the second generator tubes; means for gravitationally passing refrigerant-absorbent solution from the first generator into an upper portion of the .second shell and distributing same in drip 'form onto the second generator tubes; means for receiving condensed refrigerant from within the second generator tubes comprising a first chamber located at the outlet ends of said tubes, a second chamber, and a restricted passage between the first and second chambers for passing condensed refrigerant and flashed vapor into lthe second chamber; an additional passage between the second chamber and interior of the second generator shell to permit flashed vapor to pass into said shell; means in the second shell for collecting liquid refrigerant lformed on the condenser tubes; a third shell disposed below the .second shell and having two separate tube bundles therein; one of said last-mentioned tube bundles constituting lan evaporator, and the other constituting lan absorber; means for combining the second chamber refrigerant and condenser refrigerant; means .for distributing the combined refrigerant in drip form onto the evaporator tubes; means for collecting refrigerant-absorbent solution in the bottom of the second shell and distributing same in drip form onto the absorber tubes; and means for collecting refrigerant-absorbent solution in the bottom of the third shell and pumping same back to the first generator shell.

3. A double effect absorption refrigeration machine comprising a first generator which includes a horizontal Cil solution shell having a 4series of horizontal firetubes located below the solution level; a second horizontal shell having two horizontal tube bundles therein, one of said tube bundles forming a refrigerant generator, and the other tube bundle forming `a refrigerant condenser; said tube bundles being located below the solution level in the rst shell; means for passing refrigerant vapor from the first generator into the second generator tubes; means for gravitationally passing refrigerant-absorbent solution from the first generator int-o an upper portion of the second shell and distributing same in drip form onto the .second generator tubes; means for receiving condensed refrigerant from within the second generator tubes comprising a first chamber located at the outlet ends of said tubes, a second chamber, and a restricted passage `between the first and second chambers for passing condensed refrigerant and flashed vapor into the second chamber; an additional passage between the second .chamber and interior of the .second generator shell to permit flashed vapor to pass into said shell; means in the second shell for collecting liquid refrigerant formed on the condenser tubes; a third shell disposed below the second shell and having .two separate tube bundles therein; one of isaid lastmentioned tube bundles constituting an evaporator, and the .other constituting an absorber; means for combining lthe second chamber refrigerant and condenser refrigerant; means for distributing the combined refrigerant vin drip form onto the evaporator tubes; means for collecting refrigerant-absorbent solution in the bottom of the second shell land distributing same in drip form onto the absorber tubes; means for collecting refrigerant-absorbent solution in the bottom of the third shell and pumping same back to the first generator shell; said last-mentioned means comprising a trap and means for venting same to the first shell whereby to prevent ireverse flow from the generator during shutdown periods.

4. An absorption refrigeration machine comprising a first yhorizontal shell located at an elevated level; a second horizontal shell located at an intermediate level; la third horizont-al shell located at a lower level; a plurality of horizontal fire tubes extending within the .first shell to constitute a heat source for releasing refrigerant vapor from refrigerant-absorbent solution in the first shell, said first shell constituting a refrigerant generator; a second generator comprising a first horizontal tube bundle located in the second shell, and conduit means for passing released refrigerant from the first shell into the tubes of the first tube bundle in the second shell; conduit means for gravitationally passing refrigerant-absorbent solution from the first shell .into the second shell and onto the outer surfaces of the tubes in the first tube bundle, whereby refrigerant in the tubes of the first tube bundle is condensed and additional refrigerant is released in the second shell; .a condenser comprising a second tube bundle disposed in the second shell, .and means for passing coolant through the tubes .in the second tube bundle to condense refrigerant released in the second shell; an evaporator comprising a third tube bundle disposed in the lower shell, and means for passing a load liquid through the tubes of the third tube Ibundle; means for combining the condensed refrigerant from the first tube bundle with the refrigerant condensed on the `outer surfaces of the second tube bundle, and means for distributing the combined refrigerant over the tubes in the third tulbe bundle to be evaported by the load liquid; .an absorber comprising a fourth tube bundle in the lower shell; means for flowing a coolant through the tubes of the fourth tube bundle; means for gravitationally directing .solution from the second shell over the tubes in the fourth tube bundle to cause evaporated refrigerant to be absorbed into the solution; and means including a pump for passing solution from .the lower .shell into the elevated shell, said lastmentioned means including a trap for preventing backilow from the elevated shell into the lower shell.

5. In .an absorption refrigeration machine, the combination comprising a first horizontal solution shell, and a series of horizontal fire tubes located therein below the solution Ilevel for generating refrigerant vapor; a second horizontal shell having a first tube bundle therein located below the solution level in :the rst shell; conduit means for passing refrigerant vapor from the rst shell into the tubes of the first tube bundle to effect vapor condensation; second conduit means initiating at the first shell adjacent the solution surface level for gravitationally passing solution around the outer surfaces of the It-ubes in the first tube bundle to thus release additional refrigerant from th-e solution; a second horizontal tube bundle in the second shell; means for passing coolant through the tubes of said second tube bundle to condense refrigerant which has been released in the second shell; chamber means for receiving condensed refrigerant from the tubes of the first tube bundle, and a passage between the chamber means and the interior of the second shell to permit flashed vapor to pass into the second shell.

6. An absorption refrigeration machine comprising a rst genenator having a normal solution level therein, means for heating the solution comprising a series of horizontal heat exchange ytubes located in the genenator below the solution level; a second generator comprising a first horizontal tube bundle; a conduit receiving overow solution from the first -generator and directing same around the tubes of the first tube bundle; means 'for passing refrigerant vapor released in the rst generator through the tubes of lthe first tube bundle whereby refrigerant is condensed Within :the tubes of the first tube bundle and refrigerant is released I.from solution flowing around the tubes of the first tube bundle; a condenser comprising a second horizontal tube bundle, the tubes of which have their outer surfaces exposed to t'he vapor released by the second generator; means defining a chamber located to receive refrigerant from the tubes of the first tube bundle; a passage between the chamber and the space surrounding the second tube bundle to permit flashed vapor from the chamber to condense on the outer surfaces of the tubes of the second tube bundle; an evaporator comprising a third tube bundle arranged to give up heat to refrigerant owing from Ithe condenser and said chamber; an absorber comprising a fourth tube bundle; and means for passing solution from the absorber to the first generator, said las -menltioned means including a trap for trapping solution in the first generator after shutdown of lthe machine.

7. The machine of claim 6 and further comprising a vent 'connection between an upper portion of t'he tnap and la portion of the first generator above its normal solution level.

References Cited by the Examiner UNITED STATES PATENTS 2,272,856 2/1942 Thomas 62--101 2,284,691 6/1942 Sitrandberg 62--101 2,548,287 4/1951 Blake 122-75 2,755,635 7/1956 Bourne 62-485 X 2,983,110 5/1961 Leonard 62-485 X 3,137,144 6/1964 Kaufman etal. 62-497 X 3,146,604 9/1964 Swearingen 62-489 X ROBERT A. OLEARY, Primary Examiner.

N. R. WILSON, Assistant Examiner. 

1. IN AN ABSORPTION REFRIGERATION MACHINE COMPRISING A FIRST GENERATOR AND A SECOND GENERATOR ARRANGED SO THAT REFRIGERANT VAPOR FROM THE FIRST GENERATOR AND REFRIGERANTABSORBENT SOLUTION FROM THE FIRST GENERATOR PASS IN HEAT EXCHANGE RELATION WITH ONE ANOTHER IN THE SECOND GENERATOR TO RELEASE ADDITIONAL REFRIGERANT VAPOR FROM THE SOLUTION: THE IMPROVEMENT COMPRISING THE FORMATIION OF THE FIRST GENERATOR AS A FIRST HORIZONTAL SOLUTIION SHELL HAVING A SERIES OF HORIZONTAL FIRETUBES LOCATED BELOW THE SOLUTION LEVEL; SAID SECOND GENERATOR COMPRISING A SECOND HORIZONTAL SHELL, AND A SERIES OF HEAT EXCHANGE TUBES EXTENDING WITHIN THE SECOND SHELL BELOW THE SOLUTION LEVEL IN THE FIRST SHELL; MEANS FOR PASSING REFRIGERANT VAPOR FROM THE FIRST GENERATOR INTO THE SECOND GENERATOR TUBES; CONDUIT MEANS FOR GRAVITATIONALLY PASSING LIQUID REFRIGERANT-ABSORBENT SOLUTION FROM THE FIRST SHELL INTO THE SECOND SHELL AND OVER THE OUTER SURFACES OF THE SECOND GENERATOR HEAT EXCHANGE TUBES TO RELEASE REFRIGERANT FROM THE SOLUTION; MEANS FOR RECEIVING CONDENSED REFRIGERANT FROM THE SECOND GENERATOR TUBES COMPRISING A FIRST CHAMBER LOCATED AT THE OUTLET ENDS OF THE TUBES, A SECOND CHAMBER, AND A RESTRICTED PASSAGE BETWEEN THE FIRST AND SECOND 